Collisionless Reconnection: Dynamics and Geometry

A. Bhattacharjee, N. Bessho, K. Germaschewski, and C.-S. Ng 

Space Science Center, University of New Hampshire, Durham, NH 03824


　　　Recent developments in the theory and simulation of collisionless reconnection,
governed by the generalized Ohm's law, hold the promise for providing solutions to some
outstanding problems in laboratory, space and astrophysical plasma physics.  Examples
of such problems are sawtooth oscillations in tokamaks, magnetotail substorms and solar
flares, each of which exhibit a strong impulsive character.  In each of these problems, a
key issue is the identification of fast reconnection rates that are weakly dependent on the
mechanism that breaks field lines (resistivity and/or electron inertia).  The crucial issue of
the scaling of the reconnection rate, and its dependence on plasma parameters and the
system size, is addressed by means of Hall MHD and PIC simulations as well as
nonlinear analytical models.  Connections are made with existing observations on
reconnection rates.  The applications of the theory to electron-positron plasmas, which
are of laboratory as well as astrophysical interest, brings out new issues and raises
interesting questions about the essential physics underlying fast reconnection in
collisionless systems.